Patent Application

App. No. 15/782,066

Abstract

Claims (33)

1 . A process for fracturing a subterranean geological formation comprising introducing into the formation an aqueous fracturing fluid containing an aqueous carrier liquid and a modified proppant comprising a proppant substrate particle and a hydrogel polymer coating on the proppant substrate particle, wherein the hydrogel polymer coating comprises the combination of a cationic polyacrylamide polymer and an anionic polyacrylamide polymer, and further wherein prior to reaching its final destination downhole the modified proppant is exposed to a level of water hardness which is sufficient to adversely affect the ability of said anionic polyacrylamide polymer to swell.

2 . The process of claim 1 , wherein prior to reaching its final destination downhole the modified proppant is exposed to a level of water hardness of at least 300 ppm.

3 . The process of claim 2 , wherein the aqueous carrier liquid from which the aqueous fracturing fluid is made has a level of water hardness of at least 300 ppm.

4 . The process of claim 2 , wherein the modified proppant encounters geological formation water prior to reaching its final destination downhole, and further wherein the geological formation water has a level of water hardness of at least 300 ppm.

5 . The process of claim 2 , wherein the hydrogel polymer coating comprises about 70 to 90 wt. % cationic polyacrylamide polymer and about 10 to 30 wt. % anionic polyacrylamide polymer.

6 . The process of claim 5 , wherein the modified proppant is made by (a) forming a premix of a cationic polyacrylamide polymer invert emulsion and an anionic polyacrylamide polymer invert emulsion, (b) combining the premix so formed with the proppant substrate particle with mixing, thereby forming a polymer/particle mixture, (c) continuing to mix the polymer/particle mixture until the hydrogel polymer coating is formed, and (d) drying the hydrogel polymer coating.

7 . The process of claim 6 , wherein the hydrogel polymer coating is crosslinked by means of a covalent crosslinking agent.

8 . The process of claim 7 , wherein the proppant substrate particle is coated with a first covalent crosslinking agent before the polymer/particle mixture is formed and further wherein a second covalent crosslinking agent is combined with the polymer/particle mixture before the hydrogel polymer coating is dried.

9 . The process of claim 5 , wherein the hydrogel polymer coating is made by (a) combining the proppant substrate particle with a cationic polyacrylamide polymer invert emulsion to form a first polymer/particle mixture, (b) combining the first polymer/particle mixture so formed with an anionic polyacrylamide polymer invert emulsion to form a second polymer/particle mixture, (c) continuing to mix the second polymer/particle mixture until the hydrogel polymer coating is formed, and (d) drying the hydrogel polymer coating.

10 . The process of claim 9 , wherein the hydrogel polymer coating is crosslinked by means of a covalent crosslinking agent.

11 . The process of claim 10 , wherein the proppant substrate particle is coated with a first covalent crosslinking agent before the first polymer/particle mixture is formed and further wherein a second covalent crosslinking agent is combined with the second polymer/particle mixture before the hydrogel polymer coating is dried.

12 . The process of claim 5 , wherein the hydrogel polymer coating is made by (a) combining the proppant substrate particle with an anionic polyacrylamide polymer invert emulsion to form a first polymer/particle mixture, (b) combining the first polymer/particle mixture so formed with cationic polyacrylamide polymer invert emulsion to form a second polymer/particle mixture, (c) continuing to mix the second polymer/particle mixture until the hydrogel polymer coating is formed, and (d) drying the hydrogel polymer coating.

13 . The process of claim 12 , wherein the hydrogel polymer coating is crosslinked by means of a covalent crosslinking agent.

14 . The process of claim 13 , wherein the proppant substrate particle is coated with a first covalent crosslinking agent before the first polymer/particle mixture is formed and further wherein a second covalent crosslinking agent is combined with the second polymer/particle mixture before the hydrogel polymer coating is dried.

15 . The process of claim 5 , wherein the modified proppant exhibits a volumetric expansion of at least about 1.3 after having been subjected to shear mixing in a simulated hard water containing 6,400 ppm hardness at a shear rate of about 511 s −1 for 10 minutes.

16 . A process for fracturing a subterranean geological formation comprising introducing into the formation an aqueous fracturing fluid containing an aqueous carrier liquid and a modified proppant comprising a proppant substrate particle and a hydrogel polymer coating on the proppant substrate particle, wherein the hydrogel polymer coating comprises the combination of a starch and either a cationic polyacrylamide polymer or an anionic hydrogel polymer, and further wherein prior to reaching its final destination downhole the modified proppant is exposed to a level of water hardness which is sufficient to adversely affect the ability of said anionic hydrogel polymer to swell.

17 . The process of claim 16 , wherein prior to reaching its final destination downhole the modified proppant is exposed to a level of water hardness of at least 300 ppm.

18 . The process of claim 17 , wherein the aqueous carrier liquid from which the aqueous fracturing fluid is made has a level of water hardness of at least 300 ppm.

19 . The process of claim 18 , wherein the modified proppant encounters geological formation water prior to reaching its final destination downhole, and further wherein the geological formation water has a level of water hardness of at least 300 ppm.

20 . The process of claim 16 , wherein the hydrogel polymer coating comprises the combination of a nonionic starch and a cationic polyacrylamide polymer.

21 . The process of claim 16 , wherein the hydrogel polymer coating comprises the combination of a hydrolyzed starch and an anionic hydrogel polymer.

22 . The process of claim 16 , wherein the modified proppant exhibits a volumetric expansion of at least about 1.3 after having been subjected to shear mixing in a simulated hard water containing 6,400 ppm hardness at a shear rate of about 511 s −1 for 10 minutes.

23 . A modified proppant comprising a proppant substrate particle and a hydrogel polymer coating on the proppant substrate particle, wherein the hydrogel polymer coating comprises the combination of a starch and either a cationic polyacrylamide polymer or an anionic hydrogel polymer.

24 . The modified proppant of claim 23 , wherein the hydrogel polymer coating comprises the combination of a nonionic starch and a cationic polyacrylamide polymer.

25 . The modified proppant of claim 23 , wherein the hydrogel polymer coating comprises the combination of a hydrolyzed starch and an anionic hydrogel polymer.

26 . The modified proppant of claim 23 , wherein the hydrogel polymer coating is crosslinked by means of a covalent crosslinking agent.

27 . The modified proppant of claim 23 , wherein the modified proppant exhibits a volumetric expansion of at least about 1.3 after having been subjected to shear mixing in a simulated hard water containing 6,400 ppm hardness at a shear rate of about 511 s −1 for 10 minutes.

28 . A process for fracturing a subterranean geological formation comprising introducing into the formation an aqueous fracturing fluid containing an aqueous carrier liquid and a modified proppant comprising a proppant substrate particle and a hydrogel polymer coating on the proppant substrate particle, wherein the hydrogel polymer coating comprises the combination of a cationic polyacrylamide polymer or an anionic polyacrylamide polymer, wherein the amount of the anionic polymer to total polymer is less than about 50 wt % on a dry weight basis, the amount of the cationic polymer to total polymer is at least about 50% wt % on a dry weight basis and the hydrogel polymer coating is crosslinked by means of a covalent crosslinking agent.

29 . The process of claim 28 , wherein the aqueous carrier liquid from which the aqueous fracturing fluid is made has a level of water hardness of at least 300 ppm.

30 . The process of claim 28 , wherein the hydrogel polymer coating is made by (a) combining the proppant substrate particle with a cationic polyacrylamide polymer invert emulsion to form a first polymer/particle mixture, (b) combining the first polymer/particle mixture so formed with an anionic polyacrylamide polymer invert emulsion to form a second polymer/particle mixture, (c) continuing to mix the second polymer/particle mixture until the hydrogel polymer coating is formed, (d) adding a covalent crosslinking agent and (e) drying the hydrogel polymer coating.

31 . The process of claim 28 wherein the covalent crosslinking agent is polymeric methylenediphenyldiisocyanate.

32 . The process of claim 28 wherein the amount of the anionic polymer to total polymer is less than about 30 wt % on a dry weight basis, the amount of the cationic polymer to total polymer is at least about 70% wt % on a dry weight basis.

33 . The process of claim 30 wherein the proppant substrate is pretreated with a solution of polyethylenediglycidyl ether prior to combining the particle with a cationic polyacrylamide polymer invert emulsion.

Assignments (8)